The invention relates to a method of separating fission molybdenum from other fission products in an aqueous solution of the fission products.
Such a method is just one step in the production process for fission molybdenum in which first nuclear fuel (for example a uranium-aluminum alloy essentially with the composition U Al.sub.3 encased in aluminum) is irradiated in a nuclear reactor whereby the fission products are generated from the uranium. Of the fission products generated thereby, the fission molybdenum and particularly the isotope .sup.99 Mo is of particular interest since, from the isotope .sup.99 Mo, by radioactive decay, the radioactive isotope .sup.99m Tc is formed, which is used in the medicine for the diagnosis of organ function failures and also for the treatment of tumors.
During reprocessing, the irradiated nuclear fuel is first treated with an alkaline solution whereby the aluminum and a number of fission products, such as antimony, iodine, tin, tellurium, as well as the sought-for molybdenum, are dissolved. In several subsequent method steps, the molybdenum is then separated from the accompanying fission products. For this separation, a separation process has been developed in the German Nuclear Rese, arch Center at Karlsruhe, wherein chromatographic columns are utilized.
In this process, the alkaline solution of the fission products passes through a first column which comprises a lightly basic exchanger (AG 1.times.8, 50-500 mesh). In this step, the molybdenum, together with some of the other fission products, are quantitatively retained in the column while a large part of the unwanted fission products passes through the column.
After several purification steps, the molybdenum and small amounts of accompanying other fission products are dissolved and removed from the columns by elutriation with 1-1.5M sulfuric acid and, subsequently, with 0.5M ammonium hydroxide and 1M sodium sulfate.
Rhodanide ions and reduction agents (potassium iodide and sodium sulfite) are admixed to the solution. Under these conditions, a molybdenum complex [Mo(SCN).sub.6 ].sup.3- is formed. This molybdenum complex can be selectively bound, for example, in the manner as described in DE 23 10 948 A1 or in DE 27 58 783 C3, to an organic ion exchanger such as a chelate-forming resin on a methylen-nitrilo-diacetate-group basis (CHELEX), whereby the impurities of the fission molybdenum are effectively removed.
The process outlined above is described in great detail in the publication "Production of Molybdenum--99" by Sameh A. All in the Proceedings International Symposium on Isotope Applications, Taipei, Taiwan, Republic of China (Dec. 4-5, 1986, Pages 291-303 and also, to some extent, in DE--OS 27 58 783.
It is very important that all process steps are performed rapidly and efficiently in such a reprocessing process since the desired fission isotope .sup.99 Mo decays quickly. The yield does not only depend on the efficiency of the process steps, but also on the time needed to execute the process. For this reason, one also tries to keep the volume of the solutions to be treated as small as possible. Any small step which results in an improvement in this respect and which can be easily integrated in the existing reprocessing process or by which existing processing steps can be easily replaced is, therefore, of commercial interest.
Such a step is represented by a process of the type described earlier. This process is described in detail in the publication by J. Burck, Sameh A. Ali and H. J. Ache entitled "Sorption Behavior of Molybdenum on Different Metal Oxide Ion Exchangers" in Solvent Extraction and Ion Exchange, 6(1)(1988) pages 167-182. In this publication, the molybdenum-retaining capability of a solid bed consisting of metal oxides (aluminum oxide, tin oxide, manganese dioxide, antimony oxide) is investigated. Although the molybdenum retaining capability of a solid bed of manganese dioxide was found to be very high, the authors conclude (on page 177) that such a solid bed is not suitable for the separation of molybdenum because of its sensitivity to mechanical wear: When molybdenum-containing solutions were treated with manganese dioxide, very fine molybdenum-charged particles were found which could not be filtered out of the liquid phase and which therefore resulted in high losses of fission molybdenum.
From DE 31 00 365 A1 and World Patent Index AN:88-04109016, it is known to separate fission molybdenum from aqueous solutions by adsorption to manganese dioxide, which is disposed on an aluminum oxide or silica gel carrier.
It is the object: of the present invention to modify the process described earlier in such a way that it can be used for the separation of the fission molybdenum from other fission products and to minimize or fully eliminate especially the molybdenum losses which occur because the very fine molybdenum loaded particles are not retained in a manganese dioxide solid bed. Furthermore, it should be possible to integrate the process into the above described reprocessing process in such a way that the reprocessing speed and efficiency is increased.